This invention relates to a combustion cylinder structure for an oil burner, and more particularly to a combustion cylinder structure for an oil burner which is adapted to discharge heat rays emitted from red-heated inner and outer combustion cylindrical members through a heat-permeable cylinder to the exterior.
Conventionally, there is known a combustion cylinder structure for an oil burner which is constructed in such a manner that a heat-permeable cylinder is arranged outside a double-cylinder combustion means including an inner cylindrical member and an outer cylindrical member each formed with a plurality of small through-holes, so that fuel oil vaporized from a wick is thermally decomposed to produce combustible gas in a first space between both cylindrical members, which is then burned in the combustion means while rising in the first space to red-heat both cylindrical members, resulting in heat rays being radiated therefrom through the heat-permeable cylinder to the exterior of the oil burner for heating. The combustion of the vaporized fuel oil is carried out near the through-holes of the cylindrical members using combustion air supplied through the through-holes of the cylindrical members to the first space. In the so-constructed combustion cylinder structure, it is carried out to vary a pressure balance in order to causes a part of the combustible gas to be discharged, together with a part of flame formed in the first space, from the first space via the through-holes of the outer cylindrical member to the outside of the outer cylindrical member or a second space between the outer cylindrical member and the heat-permeable cylinder. In this instance, where the through-holes of the outer cylindrical member are formed into a small diameter, the flame is cooled by the outer cylindrical member at the time when it passes through the through-holes of the outer cylindrical member, resulting in being extinguished. This leads to the generation of incomplete combustion gas.
In order to avoid such a problem, it is proposed that the through-holes of the outer cylindrical member are formed into a larger diameter so as to facilitate the migration or leakage of the flame and gas from the first space to the second space. Such construction is considered to eliminate the deterioration of red-heating of the outer cylindrical member which is caused due to the cooling of the outer surface of the outer cylindrical member by combustion air rising along the outer surface, because a part of the combustible gas leaking to the outside of the outer cylindrical member is burned on the outer surface of the outer cylindrical member to surround the outer surface with a flame produced by the combustion.
Unfortunately, actually it is highly difficult or substantially impossible to control the amount of the combustible gas leaking to the outside of the outer cylindrical member. For example, when the combustible gas leaks in an amount which cause the flame to be lifted out of the through-holes of the outer cylindrical member, the flame is cooled by combustion air of a low temperature, resulting in being partially extinguished to lead to the generation of incomplete combustion gas. As an approach to the problem, it would be considered to burn the so-generated incomplete combustion gas at the upper section of the first space between the inner cylindrical member and the outer cylindrical member.
However, combustion gas containing the so-generated incomplete gas is diffused throughout the second space between the outer cylindrical member and the heat-permeable cylinder, therefore, the conventional combustion cylinder structure causes at least a part of the incomplete combustion gas to be exhausted to the exterior of the oil burner without being subjected to complete combustion. This occurs particularly when the wick is lowered for a small amount of combustion, because the combustion at this time is substantially carried out at a lower section of the first space.
In order to eliminate such a disadvantage, in the conventional combustion cylinder structure, it is proposed to form the lower through-holes of the outer cylindrical member into a smaller diameter and arrange an inward collar of an annular shape on the inner surface of a heat-impermeable cylinder in a manner to inward extend toward the outer cylindrical member to define an annular gap between the collar and the outer cylindrical member, as disclosed in Japanese Patent Publication No. 55083/1982. More particularly, as shown in FIG. 1, a heat-impermeable cylinder 100 on which a heat-permeable cylinder 102 is supported is provided with a collar 104 of an annular shape in a manner to inward extend from the cylinder 102 toward a perforated outer cylindrical member 106 to define a gap 108 between the outer cylindrical member 106 and the collar 104, so that combustion air may be positively supplied to a first space 110 between a perforated inner cylindrical member 112 and the outer cylindrical member 106, resulting in the positive combustion of the combustible gas in the first space 110 when a wick is lowered for a small amount of combustion.
However, such construction of the combustion cylinder structure causes the maximum combustion or heating capacity of the structure to be substantially decreased, because the collar 104 substantially restricts the amount of combustion air supplied to a second space 114 defined between the outer cylindrical member 106 and the heat-permeable cylinder 102 through a space between the heat-impermeable cylinder 100 and the outer cylindrical member 106. In order to avoid such a problem, it would be considered to expand the gap 108. However, this causes a large amount of air to readily rise in the second space 114, so that the amount of air to be supplied to the first space 110 is highly reduced to a degree sufficient to cause incomplete combustion in the first space 110.
Thus, the conventional combustion cylinder construction renders an increase in size or width of the gap 108 substantially impossible. Substitutively, the upper through-holes of the outer cylindrical member 106 are formed into a larger diameter to guide a part of the combustible gas from the first space to the second space 114 for burning it in the upper section of the second space 114, to thereby prevent a reduction in maximum combustion capacity of the structure.
Nevertheless, in the conventional combustion cylinder structure, the above-described construction of the collar 104 causes a part of combustion air supplied through the gap 108 to the second space 114 to whirl above the collar 104 as indicated by arrows in FIG. 1, leading to a turbulent flow, which cooperates with another part of the combustion air rising in the second space 114 to spread or diffuse combustion gas produced on the outer surface of the outer cylindrical member 106 throughout the second space 114, so that the control of combustion in the combustion cylinder structure is restricted to a significant degree.
Also, it is proposed that the conventional combustion cylinder construction is provided with a central cylinder in a manner to be suspended from an annular top plate of the inner cylindrical member to a position of a red-heated section of the double-cylinder combustion means for the purpose of improving the red-heating of the combustion means, as disclosed in Japanese Utility Model Publication No. 32101/1976. The arrangement of such a central cylinder permits air supplied to a gap or space between the inner cylindrical member and the central cylinder to be uniformly supplied via the through-holes of the inner cylindrical member to the first space between the inner cylindrical member and the outer cylindrical member, as well as prevents air upward supplied through the central cylinder to a flame spreading means or re-combustor from adversely affecting the red-heating of the double-cylinder combustion means.
In the combustion cylinder structure of such construction, when the wick is lowered for a small amount of combustion during the combustion operation, the burning of combustible gas produced due to the thermal decomposition of fuel oil vaporized from the wick such as hydrocarbon of a low molecular weight, carbon monoxide and the like is substantially completed in the first space between the inner cylindrical member and the outer cylindrical member. At this time, air supplied from the lower end of the oil burner through its interior to the gap between the central cylinder and the inner cylindrical member is then supplied via the through-holes of the inner cylindrical member to the first space. Accordingly, when the wick is lowered to a degree sufficient to cause the combustion of the combustible gas to be completed in the first space, air upward flowing through the space between the inner cylindrical member and the central cylinder tends to be readily guided via the upper through-holes of the inner cylindrical member to the upper section of the first space, so that air supplied to the lower section of the first space is decreased to a degree sufficient to cause the incomplete combustion of the combustible gas.